Concrete is gravel, sand, cement, lyme, and water, mixed in various ratios.
There’s a lot of variations and additives that can change how quickly it cures, often to speed it up or slow it down to account for weather (temperature and humidity play a huge part in how it cures), or to modify the pace of how it cures so you can keep building on it if you’re building vertically.
It’s a simple concept that gets incredibly complicated very quickly.